1. Field of the Invention
The present invention relates to a gas measuring apparatus and a gas measuring method.
2. Description of the Related Art
In non-patent document 1 (R. Harig and G. Matz, Field Analytical Chemistry and Technology, Vol. 5 (1-2), and pp. 75-90, 2001), there is described a technique in which a processing section identifies a measuring object gas by using a remote gas spectroscopic imaging detector (hereinafter simply referred to as “detector”) having a scanning mirror, an optical system, a Fourier spectrometer, and a single element infrared sensor, and measures the spatial distribution and density of the measuring object gas.
For example, in non-patent document 1, there is described a technique in which the temperature of the measuring object gas and the background temperature of the measuring object gas (hereinafter simply referred to as “background temperature”) are detected on the basis of the output of the detector, and in which the measuring object gas is identified by using the temperature of the measuring object gas and the background temperature.
The temperature of the measuring object gas and the background temperature are detected as follows.
The processing section first generates infrared spectrum data from the output of the single element infrared sensor. Then, the processing section converts the infrared spectrum data to radiance temperature spectrum data.
The processing section uses, as the background temperature, the maximum radiance temperature in the radiance temperature spectrum data.
The radiance temperature maximum value in the radiance temperature spectrum data corresponds to data of a substance having the highest transmittance (substance which almost transmits light from the background) among substances which exist between the detector and the background of the measuring object gas, that is, corresponds to data of light from the background. For this reason, it is thought that the radiance temperature maximum value most faithfully represents the background temperature among the radiance temperature spectrum data.
Then, the processing section uses, as the temperature of the measuring object gas, the minimum radiance temperature in the wavelength band near the wavelength of 14.5 micrometers in the radiance temperature spectrum data.
The wavelength band near the wavelength of 14.5 micrometer corresponds to the strong absorption band of CO2 (carbon dioxide). For this reason, a part of the light from the background of the measuring object gas having a wavelength near 14.5 micrometers is absorbed by CO2. Therefore, the radiance temperature near the wavelength of 14.5 micrometers in the radiance temperature spectrum data does not depend on the light from the background of the measuring object gas but depends on the amount of absorption by CO2. Further, in the case where the amount of absorption by CO2 is very large, the radiance temperature near the wavelength of 14.5 micrometers in the radiance temperature spectrum data represents the temperature of CO2 gas itself.
Therefore, it is thought that the minimum radiance temperature near the wavelength of 14.5 micrometers in the radiance temperature spectrum data represents the temperature of CO2. At present, CO2 universally exists in the earth's atmosphere. Therefore, it is thought that the temperature of CO2 represents the temperature of the earth's atmosphere. The measuring object gas also exists in the earth's atmosphere. For this reason, it is considered that the temperature of the measuring object gas becomes equal to the temperature of the earth's atmosphere, that is, the temperature of CO2.
The processing section described in non-patent document 1 measures the temperature of the object gas by using CO2 which has a strong absorption band near the wavelength of 14.5 micrometers.
For this reason, the technique described in non-patent document 1 has a restriction in which it is necessary to use, as the infrared sensor, an infrared sensor which is capable of detecting an infrared ray having a wavelength at least up to 14.5 micrometer.
Therefore, in the technique described in non-patent document 1, the usable infrared sensor is restricted, and thereby it is not possible to use, for example, a two-dimensional infrared detector having a cutoff wavelength of 11 micrometer.